Continuous phenol-aldehyde,polycondensation process

ABSTRACT

THE PROCESS IS INTENDED FOR MANUFACTURING PHENOL RESINS. THE REACTION BETWEEN PHENOL AND ALDEHYDE IS CARRIED OUT IN AN AQUEOUS SOLUTION WHEREIN PRIMARY RESINOUS REACTION PRODUCTS ARE PERSENT IN A DISPERSED PHASE. THE TIME OF RESIDENCE OF SAID RESINOUS PRODUCTS IN THE REACTION VESSEL DOES NOT EXCEED SUBSTANTIALLY THE TIME REQUIRED FOR THEIR SEDIMENTATION FROM THE SOLUTION. THE REMOVAL OF THE RESINOUS PRODUCTS PRACTICALLY AS THEY FORM MAKES IT POSSIBLE TO INTENSIFY THE REACTION WITHOUT SUBSTANTIALLY INCREASING THE DEGREE OF POLYCONDENSATION OF SAID PRODUCTS. THE CONVERSION OF THE PRIMARY RESINOUS PRODUCTS TO RESIN WITH A REQUIRED DEGREE OF POLYCONDENSATION IS EFFECTED AFTER THE SEPARATION OF SAID PRODUCTS FROM THE AQUEOUS SOLUTION BY MAINTAINING IT AT AN ELEVATED TEMPERATURE, WHICH PROVIDES FOR AN ACCURATE CONTROL OF THE DEGREE OF POLYCONDENSATION OF THE RESIN, AND CONTRIBUTES TO THE OBTAINING OF THE RESIN OF A HOMOGENOUS COMPOSITION,

June 18, 1974 p.51 IVANOV ETAL 3,817,923

CONTINUOUS PHENOL-ALDEHYDE, rowcounsnsmron PROCESS Original Filed May2'7, 1970 United States Patent Ofice.

3,817,923 Patented June 18, 1974 3,817,923 CONTINUOUS PHENOL-ALDEHYDE,POLYCONDENSA'I'ION PROCESS Petr Sergeevich Ivanov and VladimirMikhailovich Demkin, both of Moscow, U.S.S.R. Continuation ofapplication Ser. No. 40,822, May 27, 1970, which is acontinuation-in-part of abandoned application Ser. No. 494, Jan. 2,1970, which is a continuation of abandoned application Ser. No. 755,005,Aug. 27, 1968, which in turn is a continuation of abandoned applicationSer. No. 412,409, Nov. 19, 1964. This application June 5, 1972, Ser. No.259,901

Int. Cl. C08g 5/06 US. Cl. 260-57 C 6 Claims ABSTRACT OF THE DISCLOSUREThe process is intended for manufacturing phenol resins. The reactionbetween phenol and aldehyde is carried out in an aqueous solutionwherein primary resinous reaction products are persent in a dispersedphase. The time of residence of said resinous products in the reactionvessel does not exceed substantially the time required for theirsedimentation from the solution. The removal of the resinous productspractically as they form makes it possible to intensify the reactionwithout substantially increasing the degree of polycondensation of saidproducts. The conversion of the primary resinous products to resin witha required degree of polycondensation is effected after the separationof said products from the aqueous solution by maintaining it at anelevated temperature, which provides for an accurate control of thedegree of polycondensation of the resin, and contributes to theobtaining of the resin of a homogeneous composition.

This application is a continuation of co-pending application Ser. No.40,822 filed May 27, 1970 now abandoned. The latter application was acontinuation-in-part of Ser. No. 494 filed Jan. 2, 1970 now abandonedwhich in turn is a continuation of application Ser. No. 755,005 filedAug. 23, 1968 now abandoned which in turn is a continuation ofapplication Ser. No. 412,409 filed Nov. 19, 1964 now abandoned.

DETAILED DESCRIPTION (1) The present invention relates to the productionof phenol-aldehyde resins, and more specifically represent an improvedcontinuous process of phenol-aldehyde polycondensation.

(2) As is known, polycondensation of phenol with aldehyde is acomplicated system of successive and parallel processes of interactionbetween the reactants. In the entire variety of these processes twoprocesses prove to be most important for the commercial production ofthe resin namely, binding of phenol and aldehyde with the formation ofprimary resinous products, and conversion of said primary products toresin due to the reaction of growth of the polymer chain. The first ofthe said processes is essentially responsible for the degree ofconversion of the starting reactants, that is, for the completeness ofutilization of raw materials; therefore, it has a substantial influenceon the cost price of the resin. Hence, it is obvious, that said firstprocess is desirable to be carried out in such a manner that the degreeof conversion of the reactants be maximum. The second of the saidprocesses is responsible for the degree of polycondensation and for thepolymer-homologous composition of the resin, and, hence, for the qualityof the resultant product.

In this connection, the said second process should be carried out insuch a way, that the resin obtained should feature a required degree ofpolycondensation, it being also desirable that maximum similarity of theresin molecules be attained.

A common feature characteristic for both batch and continuous methods ofpolycondensation in tubular reactors (U.S. Pat. No. 1,660,403 toTerkington), in mixing reactors comprising one vessel (U.S. Pat. No.2,688,- 606 to Schmitt et al.) or a plurality of series-connectedvessels (U.S. Pats. Nos, 2,616,872 and 2,663,699 to Bloem et al.) andalso for a method of selective" polycondensation (U.S. Pat. No.2,750,354 to Merriam) is that both said processes are carried outsimultaneously in the same reaction zone. As consequence, the both saidprocesses take place under essentially the same reaction conditions.However, the optimum conditions for carrying out each of said processesare essentially different and, to a certain extent, mutually exclusive.

In deed, for attaining maximum degree of conversion of the reactants, itis obviously reasonable to use such conditions which intensify thereactions of binding said reactants with the formation of resin-formingpolycondensation products, that is, an increase of the temperature inthe reactor, an increase of the concentration of the catalyst in thereaction mass, etc.

These intensifying conditions, however, simultaneously stimulate anincrease in the rate of the reactions of the growth of the polymerchain, whereby the degree of polycondensation of the resin increases.

As a result, within the framework of the above-mentioned methods ofpolycondensation, the possibility of intensifying the reaction forincreasing the degree of conversion of the reactants or for decreasingthe volume of the reaction zone with a view to cutting down specificcapital investments proves to be rather limited, since any considerableintensification leads to the obtaining of resin with an inadmissiblyhigh degree of polycondensation, or even to gelatinization of the resindirectly in the reactor.

On the contrary, sufficiently moderate conditions of carrying out thereaction make possible an accurate control of the degree ofpolycondensation and, moreover, contribute to the obtaining of the resinof a more homogeneous composition.

Thus, when carrying out polycondensation according to any of the knownmethods, a problem inevitably arises, which of said processes is to bepreferred, since carrying out of the reaction under sufliciently mildconditions is associated with an increase in the losses of raw materialsor at least with a considerable decrease in the throughput of theequipment, while the performance of the reaction under intensifyingconditions makes more difiicult the control of the degree ofpolycondensation of the resin, which increases the danger of obtainingthe resin with a degree of polycondensation lying outside the prescribedlimits, or even gelatinization of the resin in the reactor.

In the industrial practice the conditions adopted for carrying out thereaction are, as a rule, those of a compromise, and, to a certainextent, differ from those optimal for both of the above-said processes,or, in any case, for one of them.

An object of the present invention is to provide an intensified processof phenol-aldehyde polycondensation, which makes possible toconsiderably increase the degree of conversion of the starting reactantsas compared to the processes known heretofore.

Another object of the invention is the provision of an intensifiedprocess of polycondensation, which allows a reduction in the specificvolume of the reactor.

A further object of the invention is the provision of a process ofpolycondensation, which ensures the obtaining of resins with ahomogeneous polymer-homologous composition.

The present invention also provides a possibility for producing resinswith the use of diluted solutions featuring low concentrations of phenoland aldehyde.

Other objects and advantages of the present invention will become morefully apparent from the following description and the appendeddiagrammatic flow sheet.

In accordance with the present invention, it is proposed that theprocess of binding phenol and aldehyde with the formation of primaryresinous products should be spatially isolated from the process ofconversion of said primary products to a resin with a prescribed degreeof polycondensation, so that the first of said processes should takeplace and terminate in one reaction zone, and the second of saidprocesses should take place, mainly, and terminate in another,subsequent reaction zone. Such separation of the said processes in spaceprovides a possibility for each of these processes to be carried outunder optimal conditions.

The process of polycondensation, according to the present invention,comprises the following sequence of operations.

Phenol, aldehyde and reaction catalyst are continuously introduced intoa reaction zone which is a vessel filled with an aqueous solutioncontaining said phenol, aldehyde and catalyst.

The amount of said starting materials incoming into the vessel per unitof time is so adjusted, that as a result of the reaction there shouldform resinous products insoluble in the aqueous solution filling thereactor. The incoming materials are mixed with the contents of thevessel with such an intensity of mixing, that the continuously formingresinous products whose specific gravity is greater than the specificgravity of the solution which fills the vessel could freely precipitateinto the bottom part of said vessel. The aqueous solution together withsaid resinous products is removed from the bottom part of the vessel insuch an amount per unit of time, that the level of liquid in the vesselshould remain substantially the same. The resinous products removed fromthe vessel are separated from said aqueous solution and kept in asubsequent reaction zone at an elevated temperature over a period oftime suflicient for their conversion to a resin with a preset degree ofpolycondensation.

The preferred embodiment of the invention comprises the followingsequence of operations.

Phenol, aldehyde and reaction catalyst are continuously introduced intothe first reaction vessel of a plurality of reaction vessels comprisingat least two consecutively connected vessels, each of which is filledwith an aqueous solution containing said phenol, aldehyde and catalyst.

The amount of said starting materials incoming into said first vesselper unit of time is so adjusted, that already in the said first vesselthere should form resinous products of polycondensation which areinsoluble in the aqueous solution filling said vessel. The materialsincoming into said first reaction vessel are mixed with the contents ofthe vessel with such an intensity of mixing, that the continuouslyforming resinous products whose specific gravity exceeds that of thesolution which fills the vessel could be essentially freely precipitateinto the bottom part of said first reaction vessel. The aqueous solutiontogether with said resinous products is removed from the bottom part ofsaid first vessel at such a rate, that the level of liquid in saidvessel should remain essentially constant.

Into each subsequent vessel comprised in the abovementioned pluralityliquid is introduced that has been removed from the preceding vessel ofthe said plurality. In each subsequent vessel of said plurality theoperation of mixing the incoming liquid with the contents of the vessel,and of the removal of the aqueous solution of the reactants togetherwith the resinous products of polycondensation from the bottom part ofthe vessel are repeated, said operations in the subsequent vessels beingeffected in the same manner as in the said first vessel. The resinousproducts of polycondensation removed from the last vessel comprised inthe said plurality are separated from the aqueous solution removedtogether therewith and kept at an elevated temperature over a period oftime sufiicient for their convertion to a resin with a preset degree ofpolycondensation.

One of the methods of carrying out the process of phenolaldehydepolycondensation in accordance with the present invention is illustratedby the appended diagrammatic flow sheet.

The invention can be used for obtaining resins intended for themanufacture of moulding compositions, laminated plastics, adhesives,abrasives, etc.

The present invention makes it possible to manufacture boththermoplastic (novolac) and thermoreactive (resol) resins. To effect thepolycondensation reaction, as phenolic reactants there may be usedmonohydroxybenzene, isomers of cresol or of xylenol, dihydroxy phenolsand various combinations of said substances, including a mixture ofhomologues of phenol, known in the art as tar acids. As aldehydereactants use may be made of formaldehyde conventionally utilized as anaqueous solution, various solid polymers of formaldehyde, such asparaformaldehyde as well as acetaldehyde, furfural andhexamethylenetetramine. As a catalyst for the polycondensation reactionuse may be made of sulphuric acid, hydrochloric acid, oxalic acid,phenol-sulphonic acid, as well as sodium hydroxide, ammonium hydroxide,and a number of other acids, bases and salts.

Phenol, aldehyde and catalyst can be charged into the reactorseparately. It is also possible, that some of these substances or all ofthem be fed into the reactor as a mixture.

Any of the above-said substances can be used as solutions. Besides, usecan also be made of diluted solutions containing said substances, suchas, for example, waste water of the phenol-aldehyde resin manufacture.

Described hereinbelow is the continuous process of phenol-aldehydepolycondensation as illustrated in the appended diagram.

A preliminarily prepared mixture of phenol, aldehyde and reactioncatalyst, taken at a fixed ratio, is continuously fed at a given ratethrough a pipepline 1, provided with a valve 2, into a look box 3.

From the look box 3 the starting materials flow by gravity through apipeline 4 into a reaction vessel 5 with a conical bottom. The vessel 5is provided with a jacket 6 into which a heat carrier such as steam isintroduced for heatin the reaction mass during the starting period andfor maintaining a temperature in the vessel 5, required for carrying outthe polycondensation reaction.

Usually this reaction is carried out an an elevated temperature.However, at a sufficiently high concentration of the catalyst in thereaction mass, the polycondensation can proceed at normal and even at areduced temperature. In such a case the function of the heat-carrierintroduced into the jacket 6 will be, evidently, to remove exothermicheat of the polycondensation reaction.

The vessel 5 is provided with a stirrer 7 serving for a uniformdistribution of the continuously fed starting materials in the contentsof the vessel 5.

The reaction of polycondensation of phenol with aldehyde is known to behomophase only during the initial stages. Further a reduction in thesolutbility of the resulting resinous reaction products in the reactionmass due to a reduction of the concentration of phenol therein leads tothe separation of the mass into two phases, after which the reactionbecomes heterophase. One of the phases is an aqueous solution of theinitial reactants and the catalyst, since water is formed in the courseof the reaction and, besides, may be introduced into the reactor withthe starting materials; the other phase is constituted by the resinousproducts of polycondensation which are insoluble in said aqueoussolution.

For carrying the present invention into effect, it is necessary, thatthe process of polycondensation which proceeds in the vessel shouldcorrespond to the heterophase stage of the reaction. In other words, itis necessary, that with the fixed ratio of phenol, aldehyde andcatalyst, as well as temperature, the amount of materials incoming intothe vessel 5 per unit of time should be such as to ensure the formationin the vessel 5 of resinous products of polycondensation, insoluble inthe aqueous solution of the reactants. Since the specific gravity of theresulting resinous products exceeds the specific gravity of the aqueoussolution of the reactants, said products will tend to precipitate fromthe solution. For the realization of the present invention it is veryimportant also that the mixing of the contents of the vessel 5 by meansof the stirrer 7 should not interfere essentially with the precipitationof the continuously forming resinous products to the bottom part of thevessel. Most suitable for this purpose are paddle stirrers rotating at arate of 3050 r.p.m. Nevertheless, mixing of the reaction mass caused byits boiling is also admissible. From the bottom part of the vessel 5,the reaction mass, that is, the aqueous solution together with theresinous products, is continuously removed at a space velocity equal tothe rate of charging of the starting materials. It should be noted, thatunder the described conditions no bottom layer of resinous products canform in the vessel 5. Indeed, the volume of resinous products forming inthe vessel 5 during a given period of time is naturally smaller than thevolume of the starting materials incoming to the vessel during the sameperiod of time. Since from the bottom part of the vessel 5, whereto theresinous products precipitate, during the same period of time a volumeof liquid is removed equal to the volume of the starting materialscharged, resinous products cannot remain in the vessel in the form of alayer, since these products are continuously removed from the bottompart of the vessel, as they form, together with the aqueous solution ofthe reactants. Therefore, under stabilized conditions of operation, theaqueous solution of the reactants is found in the vessel as a continuousphase, whereas the resinous products are present in said vessel only asa dispersed sedimenting phase. As a result, the residence time of thephases in the vessel 5 is determined by various factors. Thus, theresidence time of the aqueous solution is practically equal to the ratioof the volume of the vessel 5 to the space velocity with which thissolution is formed in the vessel due to the reaction and also due to apossible introducing of water into the vessel together with thecontinously incoming starting materials.

The residence time of the resinous products in the vessel 5 does notdepend on the residence time of the aqueous solution therein, and isdetermined by rate of precipitation of particles of said products to thebottom part of the vessel. We have found said precipitation rate to be0.010.1 meter per second. Therefore, the residence time of the resinousproducts in the reaction vessel whose dimensions are such as usuallyadopted in industrial practice does not exceed 1-2 min. Due to a shortresidence time of the resinous products in the vessel 5, for increasingthe degree of conversion of the reactants, or for increasing thethroughput capacity, intensifying reaction conditions can be maintainedin said vessel, the influence of these conditions on the degree ofpolycondensation of the resinous products removed from the vessel beinginsignificant.

As can be seen from the above-stated, any degree of conversion of thestarting reactants, including a rather high one, can be attained alreadyin the vessel 5. However, when the present invention is used forproducing the resin on an industrial scale, this is known to beinexpedient.

For increasing the throughput of the equipment, or for enhancing thedegree of conversion of the reactants, it is preferable to employ aplurality of series-connected vessels. Therefore operations similar tothose carried out in the vessel 5 are repeated in vessels 8 and 9, thathave a design identical to that of the vessel 5. The only diiference 6in the operations is that instead of the mixture of starting materials,which is fed into the reaction vessel 5, the reaction mass is introducedfrom the preceding vessel into the vessels 8 and 9 through valves 10 and11 and look boxes 12 and 13, respectively.

In case the polycondensation is carried out at a boiling point of thereaction mass, which fact considerably simplifies the control of thethermal conditions in the vessels, vapours of volatile substancesevolving in the vessels 5, 8 and 9 enter via pipelines 14, 15 and 16 acommon reflux condenser 17 where they are condensed, and the condensatethrough the look box 3 and water seal 4 returns to the vessel 5.

For the reaction to be carried out at atmospheric pressure, the look box3 is made to communicate with the atmosphere by means of a pipeline 18.

It should be point out, that it is also possible to carry out thereaction under pressure to intensify the process by increasing thetemperature. It is apparent, that in this case the reaction vessels 5, 8and 9 should be rated for the adequate pressure. If the reaction iscarried out at normal or reduced temperature, there is, naturally, noneed in using the reflux condenser 17.

In the vessel 9 the process of interaction of the starting materials isessentially completed. The reaction mass is discharged from the vessel 9at the same rate as that of feeding the starting materials to the vessel5, and through a valve 19, and a look box 20 it is taken to a separatingcentrifuge 21, where the resinous polycondensation products areseparated from the aqueous solution.

A Florence flask or a settler operating in a continuous manner may alsobe used as a separating device. More over, water with some amount ofunconverted starting materials may be separated from the resinouspolycondensation products by evaporation.

From the separating centrifuge 21 the aqueous phase is directed via apipeline 22 and through a look box 23 into a sewer, or, if necessary, isdirected for purification from chemical admixtures.

Through a look box 24, a water seal 25 and a valve 26 the resinouspolycondensation products are continuously introduced into the bottompart of a vessel 27. Said vessel 27 is equipped with a steam jacket 28,adapted to maintain a temperature in the vessel, suflicient for thepolycondensation reaction to be continued, and with an anchor stirrer29.

Since in the reaction vessel 27 there take place no processes ofprecipitation, it is not necessary that said vessel should have aconical bottom. During the residence of the resinous products in thevessel 27 at an elevated temperature, an increase of the degree ofpolycondensation of the resin takes place. From the upper part of thevessel 27 the resinous products via an overflow pipe 30 through a valve31 enter a reaction vessel 32, where an operation similar to thatcarried out in the reaction vessel 27 is effected, both said vesselshaving an identical construction. The vessels 27 and 32 by means of gaspipelines 33 and 34 are connected with the reflux condenser 17 fromwhich the condensate is returned to the vessel 5. From the vessel 32,through an overflow pipe 35, resin having the desired degree ofpolycondensation is continuously discharged.

For carrying out the process of conversion of the resinous products to aresin with a prescribed degree of polycondensation, use can be made,naturally, of not only mixing reactors, but also of reactors of othertypes, such as tubular or periodic action ones.

For a better understanding of the present invention, some examples ofcarrying out polycondensation of phenol and aldehyde in accordance withthe invention are given hereinbelow byway of illustration.

Example 1 A mixture of starting components is preliminarily prepared,which contains technical tricresol, formalin and ammonia, taken in thefollowing ratios:

Kg. 100 percent cresol 1000 37 percent formalin 1000 25 percent aqueoussolution of ammonia 150 This mixture is continuously fed at a rate of600 kg. per hour into the first reaction vessel of the plant whichconsists of four such vessels connected in series. The capacity of eachvessel is 500 1. Each vessel is equipped with a paddle stirrer rotatingat a speed of 28 r.p.m., and with a steam jacket, into which steam isfed under a pressure of 3 atm. All the vessels operate under atmosphericpressure. Due to heating, in all the vessels condition of mild boilingat a temperature of about 100 C. are maintained. Vapours of volatilesubstances which evolve in the course of boiling of the reaction mass,enter a reflux condenser common to all the four vessels of the plant,the cooling surface of the condenser being 20 sq. m. Said condenserreturns the condensate into the first reaction vessel. The mixture ofthe starting components is continuously introduced into the upper partof the first vessel.

The reaction mass is continuously withdrawn from the bottommost part ofthe first reaction vessel. The rate of discharge is controlled by meansof a valve adjusted by automatic devices which maintain a constant levelof the liquid in the vessel.

The reaction mass discharged from the first vessel is continuouslypassed through the remaining reaction vessels of the plant, whichoperate similarly to and have the same design as the first vessel.

The reaction mass issuing from the bottommost part of the fourth (last)reaction vessel is continuously separated in a Florence flask having acapacity of 100 1. into an aqueous and a resinous phase. The aqueousphase which forms at a rate of 74 kg. per hour features a residualcontent of cresol of 0.9 percent and a residual content of formaldehydeof 1.6 percent, and therefore it is directed for purification fromharmful chemical substances.

The liquid resol resin produced at a rate of 526 kg. per hour has aviscosity of 460 cp. at 20 C., water content of 28% and 3.5 percent ofunconverted phenol. This resin can be used as a binder in themanufacture of fibrous moulding materials.

Example 2 Starting materials are continuously fed by proportioning pumpsfrom storage tanks for the polycondensation reaction in the followingamounts:

Kg. per hour 100 percent phenol 600 37 percent formalin 410 20 percentsulphuric acid 90 A plant illustrate in the appended diagrammatic flowsheet is used for carrying out the polycondensation process.

Each of the three consecutively connected reaction vessels in which adesired degree of conversion of the starting materials is reached, has acapacity of 500 litres and is equipped with a paddle stirrer rotating ata speed of 28 r.p.m. and with a steam jacket into which steam isintroduced under a pressure of 3 atm. In the first of said reactors atemperature of 75-80 C. is maintained automatically, whereas in thesubsequent two vessels the reraction is carried out at a temperature of100 C. All the vessels operate under atmospheric pressure, a constantlevel of liquid being maintained therein.

For the separation of the phases a separating centrifuge is used, whichhas a rotor consisting of 50 conical discs whose base diameter is 350mm. and height is 220 mm. The rotor rotates at a speed of 4500 r.p.m.

Each of the two reaction vessels, in which a desired degree ofpolycondensation of the resin is attained, has a capacity of 500 litresand is equipped with an anchor stirrer rotating at a speed of 60 r.p.m.and with a steam jacket, into which steam is supplied under a pressureof 3 atm.

The resinous polycondensation products which fill the vessels to thelevel of their overflow pipes are heated up to C.

All the five reaction vessels of the plant are connected by means ofpipelines with a condenser which is common for all the said vessels andhas a cooling surface of 20 sq. m.

The aqueous phase produced at a rate of 280 kg. per hour has a residualcontent of phenol of 1.3% and a residual content of formaldehyde of0.8%, and is a waste product of the process.

After the separation of the aqueous phase, the resinous polycondensationproducts which feature 18% of moisture and 4.8% of unconverted phenol,and whose viscosity is 580 cp. at 20 C., are continuously passed at arate of 820 kg. per hour through two consecutively connected reactionvessels for the viscosity of the resin to be increased up to thespecified value. The resin issuing from the last vessel of the plant hasa water content of 17.3%, content of unconverted phenol of 4.6%, and aviscosity after Ostwald at 20 C. of 28,600 cp.

This resin, after the evaporation of water, phenol and other volatilesubstances, and cooling, can be used as a binder for manufacturingabrasives.

Example 3 To the waste water resulting during the manufacture ofphenol-formaldehyde resins, which contains 3.2% of phenol and 2.3% offormaldehyde, a 30% hydrochloric acid is added in such amounts, that thepH of the solution should be within 1.2-1.3.

This solution is continuously fed for effecting the polycondensationreaction at a rate of 500 kg. per hour. The same plant and the sameconditions are used for carrying out the polycondensation, as in Example2, the difl'erence being only in that the temperature in all thereaction vessels of the plant is maintained to 'be 100 C., and only onevessel having a capacity of 50 litres is used for attaining a desiredviscosity of the resin.

The aqueous phase produced at a rate of 479 kg. per hour has a residualcontent of phenol of 0.4% and a residual content of formaldehyde of1.3%. The resin issuing from the last reaction vessel of the plant at arate of 21 kg. per hour has a water content of 22%, a content of phenolof 1.4%, and a viscosity after Ostwald at 20 C. of 36,200 cp.

The resultant resin is a novolac and can be added in small amounts toother novolac resins after the completion of the polycondensation stageand before the commencement of the evaporation stage. This resin canalso be used directly for producing moulding powders.

Example 4 In tar acids which contain 72% of phenol (as calculated formonohydroxybenzene), water, as Well as small amounts of pyridine basesand other admixtures, caustic soda and barium hydroxide are dissolved inamounts of 3.8 parts by weight and 1 part by weight, respectively, per100 parts by weight of phenol. This solution, preheated to 90 C., iscontinuously fed into a tubular reactor composed of tube-in-tube typeelements, at a rate of 270 kg. per hour. Simultaneously furfural heatedto C. is continuously introduced into the tubular reactor at a rate ofkg. per hour. The internal diameter of the tubes of said reactor is 50mm., and the total length of the reaction zone is 60 m. By supplying aheat-carrier into the reactor jackets, the temperature of the reactionmass at the outlet of the reactor is maintained at 150 C. From thetubular reactor the liquid is continuously fed to a vertical autoclavewhich has a capacity of 100 litres, is equipped with a jacket and apaddle stirrer rotating at a speed of 50 r.p.m. The process ofpolycondensation in said autoclave is carried out under a pressure thatis equilibrium for this temperature and reaches about atm. From thebottom part of the autoclave the reaction mass is continuouslywithdrawn, the discharge rate thereof being controlled by means of anautomatic valve in such a manner, that the autoclave should be filled to0.8 of its total capacity. The reaction mass removed from the autoclaveis continuously fed into one of the two alternately operating reactors,each having a capacity of 1 cu. m., equipped with a jacket and an anchorstirrer which rotates at a speed of 50 r.p.m.

The reactor is connected with a tubular condenser and therethrough itcommunicates with the atmosphere. The temperature of the reaction massincoming from the autoclave into the reactor is reduced down to 100 C.

vapours evolving as a result of throttling are condensed in thecondenser, and the condensate thus produced at a rate of 25 kg. perhour, which is essentially water with small amounts of phenol andfurfural, is directed to the sewer. After said reactor has been filledto 0.8 of its capacity, the feed of the reaction mass from the autoclaveis switched over to another reactor. Then the reactor containing theresinous polycondensation products is charged with 30 kg. of furfural,and the contents of the reactor are kept at a temperature of 100 C.under stirring during a period of about 40 min., till the viscosity ofthe resin becomes 3000 cp. The condenser in this case operates as areflux condenser. The resultant 830 kg. of novolac resin feature 19% ofwater, 1.2% of free phenol and 1.4% of furfural. After evaporation thisresin can be used for producing moulding powders.

Though the present invention has been described in connection withpreferred embodiments thereof, it is aparent that various changes andmodifications can be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will easilyunderstand. Such changes and modifications are to be considered asfalling within the true spirit and scope of the invention as defined inthe appended claims.

What is claimed is:

l. A process for carrying out phenol-aldehyde polycondensationcomprising continuously introducing phenol, aldehyde and a reactioncatalyst into a vessel filled with an aqueous solution containing saidreagents and catalyst, maintaining the temperature in said vessel at thevalue sufficient for carrying out polycondensation, holding the aqueoussolution of reagents in said vessel for a time sulficient for theformation of resulting resinous polycondensation products which areinsoluble in said aqueous solution, the time of holding being a functionof the volume of the vessel to the amount of material introduced intothe vessel per unit of time, mixing the reagents and catalyst newlyentering said vessel with the contents thereof at an intensity of mixingthat does not interfere with the precipitation of said resinouspolycondensation products to the bottom portion of the vessel,continuously removing a reaction mixture consisting of precipitatingresinous polycondensation products together with aqueous solution atsuch a rate that the level of the liquid in the vessel remains constantand no layer of polycondensation product is formed at the bottom of thevessel, the removal of the polycondensation products and aqueoussolution at the bottom of the vessel being the only place at whichremoval of these components is made from the vessel, separating thereaction mixture removed from the vessel to isolate the resinouspolycondensation products from the aqueous solution, and holding saidresinous products in a subsequent reaction zone at an elevatedtemperature suflicient for the continuation of polycondensation.

2. A process as claimed in claim 1 wherein the temperature in thesubsequent reaction zone is at least 50 C.

3. A process as claimed in claim 1 wherein the reaction mixture removedfrom the bottom of the vessel introduced into at least one furtherseries-connected vessel before it is introduced into said subsequentreaction zone, and repeating in said further vessel the operations ofmixing and removal of reaction mixture in the same manner as in thefirst vessel.

4. A process as claimed in claim 3 wherein the temperature in thereaction zone following the last vessel is 50 C.

5. A process as claimed in claim 1 wherein said mixing of the reagentsand catalyst newly entering the vessel with the contents thereof iseffected by stirring the contents of the vessel near the surface thereofat a rate of rotation of 30-50 f.p.m.

6. A process as claimed in claim 1 wherein the resinous products areprecipitated at a rate of about 0.01 to 0.1 meters per second and have aresidence time in said vessel less than 2 min.

References Cited UNITED STATES PATENTS 2,456,192 12/1948 Houlton 260-572,616,872 11/1952 Bloem et al 260-54 2,658,054 ll/ 1953 Coleman et al260-57 2,663,699 12/1953 Bloem et a1. 260-54 2,750,354 6/1956 Merriam260-57 FOREIGN PATENTS 1,089,936 11/ 1967 Great Britain.

HOWARD E. SCHAIN, Primary Examiner US. Cl. X.R.

